It is well known in the art to co-inject different plastic melts at the same time, and it is also known to sequentially inject different melts one after the other.
In the past, control of the flow of two or more fluids through a gate and into a cavity has been provided by rotating a valve pin member to align different fluid channels or by axially reciprocating a valve pin member and one or more valve sleeve members, which surround the valve pin member, between retracted open and forward closed positions. For example, a valve pin member can be rotated between different positions to provide coinjection or sequential injection molding.
A valve pin member and valve sleeve member can be axially reciprocated to provide coinjection or sequential injection of at least two different melts, although this is not without its problems, such as inaccuracies in reciprocating movement, difficulties in keeping the different melts adequately separated, and the problems of simplifying manufacture, assembly, and operation of the apparatus. Another problem is that it is difficult to align a valve sleeve member or a valve pin member with a cavity gate, such aligning being important for improving injection technique and reducing gate wear.